1. Field of the Invention
The present invention relates notably to a rotating electrical machine, in particular for an automotive vehicle starter.
2. Description of Related Art
The patent EP-B1-985 334 describes a starter including a stator having a plurality of magnetic poles disposed on a circumferential internal surface of a yoke. Each magnetic pole is formed by a ferrite permanent magnet that is magnetised so that the north and south poles are radially oriented. Auxiliary magnets can be provided between the aforementioned magnets. These auxiliary magnets are of ferrite and magnetised so that the north and south poles are circumferentially oriented. A space is provided between each auxiliary magnet and the yoke. Such a disposition reduces magnetic leaks.
It has been found that a strong armature magnetic reaction in a DC electrical machine with brushes, in particular in a starter having a high magnetomotive force (mmf) at very low voltages and a usable power greater than 1 kW, can lead to a reduction in the performance of the machine. In some cases, an angular offset of the brushes and/or a compensation winding or switching assistance winding are used to alleviate the effects of the armature reaction. The angular offset of the brushes is optimal only for a predetermined electric current. Also, the aforementioned winding is generally bulky.
There is also known from the paper entitled ‘The application of Halbach cylinders to brushless AC servo motors’, K. Atallah and D. Howe, IEEE Transactions On Magnetics, Vol. 34, No. 4, July 1998, a brushless machine in which the variation of the induction relative to the electrical angle in the airgap is sinusoidal. The paper ‘New concept of permanent magnet excitation for electrical machines. Analytical and numerical computation’, M. Marinescu and N. Marinescu, IEEE Transactions On Magnetics, Vol. 28, No. 2, March 1992, concerns magnetisation in a slotless type machine, the magnetic excitation being either on the rotor or on the stator of the machine.
It is known, in an automotive vehicle starter, to produce a stator, or armature, by gluing permanent magnets to a yoke of the stator. In some cases it can prove difficult to glue on permanent magnets. It is also known to fix permanent magnets to the yoke using clips, each adapted for only one permanent magnet. The patent application EP 1 035 629 and U.S. Pat. No. 6,465,925 describe examples of clips for holding auxiliary magnets between main magnets. U.S. Pat. No. 4,707,630 teaches holding permanent magnets against a yoke using a cylinder made from sheet steel bearing against an interior circumference of the permanent magnets.